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130 lines
6.8 KiB
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130 lines
6.8 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2019 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Selecting Guile Pretty-Printers (Debugging with GDB)</title>
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<meta name="description" content="Selecting Guile Pretty-Printers (Debugging with GDB)">
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<meta name="keywords" content="Selecting Guile Pretty-Printers (Debugging with GDB)">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Guile-API.html#Guile-API" rel="up" title="Guile API">
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<link href="Writing-a-Guile-Pretty_002dPrinter.html#Writing-a-Guile-Pretty_002dPrinter" rel="next" title="Writing a Guile Pretty-Printer">
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<link href="Guile-Pretty-Printing-API.html#Guile-Pretty-Printing-API" rel="prev" title="Guile Pretty Printing API">
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</head>
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<body lang="en">
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<a name="Selecting-Guile-Pretty_002dPrinters"></a>
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<div class="header">
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<p>
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Next: <a href="Writing-a-Guile-Pretty_002dPrinter.html#Writing-a-Guile-Pretty_002dPrinter" accesskey="n" rel="next">Writing a Guile Pretty-Printer</a>, Previous: <a href="Guile-Pretty-Printing-API.html#Guile-Pretty-Printing-API" accesskey="p" rel="prev">Guile Pretty Printing API</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Selecting-Guile-Pretty_002dPrinters-1"></a>
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<h4 class="subsubsection">23.3.3.9 Selecting Guile Pretty-Printers</h4>
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<a name="index-selecting-guile-pretty_002dprinters"></a>
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<p>There are three sets of pretty-printers that <small>GDB</small> searches:
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</p>
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<ul>
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<li> Per-objfile list of pretty-printers (see <a href="Objfiles-In-Guile.html#Objfiles-In-Guile">Objfiles In Guile</a>).
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</li><li> Per-progspace list of pretty-printers (see <a href="Progspaces-In-Guile.html#Progspaces-In-Guile">Progspaces In Guile</a>).
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</li><li> The global list of pretty-printers (see <a href="Guile-Pretty-Printing-API.html#Guile-Pretty-Printing-API">Guile Pretty Printing API</a>).
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These printers are available when debugging any inferior.
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</li></ul>
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<p>Pretty-printer lookup is done by passing the value to be printed to the
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lookup function of each enabled object in turn.
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Lookup stops when a lookup function returns a non-<code>#f</code> value
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or when the list is exhausted.
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Lookup functions must return either a <code><gdb:pretty-printer-worker></code>
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object or <code>#f</code>. Otherwise an exception is thrown.
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</p>
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<p><small>GDB</small> first checks the result of <code>objfile-pretty-printers</code>
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of each <code><gdb:objfile></code> in the current program space and iteratively
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calls each enabled lookup function in the list for that <code><gdb:objfile></code>
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until a non-<code>#f</code> object is returned.
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If no pretty-printer is found in the objfile lists, <small>GDB</small> then
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searches the result of <code>progspace-pretty-printers</code> of the current
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program space, calling each enabled function until a non-<code>#f</code> object
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is returned.
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After these lists have been exhausted, it tries the global pretty-printers
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list, obtained with <code>pretty-printers</code>, again calling each enabled
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function until a non-<code>#f</code> object is returned.
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</p>
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<p>The order in which the objfiles are searched is not specified. For a
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given list, functions are always invoked from the head of the list,
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and iterated over sequentially until the end of the list, or a
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<code><gdb:pretty-printer-worker></code> object is returned.
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</p>
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<p>For various reasons a pretty-printer may not work.
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For example, the underlying data structure may have changed and
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the pretty-printer is out of date.
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</p>
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<p>The consequences of a broken pretty-printer are severe enough that
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<small>GDB</small> provides support for enabling and disabling individual
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printers. For example, if <code>print frame-arguments</code> is on,
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a backtrace can become highly illegible if any argument is printed
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with a broken printer.
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</p>
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<p>Pretty-printers are enabled and disabled from Scheme by calling
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<code>set-pretty-printer-enabled!</code>.
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See <a href="Guile-Pretty-Printing-API.html#Guile-Pretty-Printing-API">Guile Pretty Printing API</a>.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Writing-a-Guile-Pretty_002dPrinter.html#Writing-a-Guile-Pretty_002dPrinter" accesskey="n" rel="next">Writing a Guile Pretty-Printer</a>, Previous: <a href="Guile-Pretty-Printing-API.html#Guile-Pretty-Printing-API" accesskey="p" rel="prev">Guile Pretty Printing API</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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